docs: def sed(filename, before, after, flags='g'):
      """
      Search and replaces the given pattern on filename.
  
      :param filename: relative or absolute file path.
      :param before: expression to be replaced (see 'man sed')
      :param after: expression to replace with (see 'man sed')
      :param flags: sed-compatible regex flags in example, to make
      the  search and replace case insensitive, specify ``flags="i"``.
      The ``g`` flag is always specified regardless, so you do not
      need to remember to include it when overriding this parameter.
      :returns: If the sed command exit code was zero then return,
      otherwise raise CalledProcessError.
      """
      expression = r's/{0}/{1}/{2}'.format(before,
                                           after, flags)
  
      return subprocess.check_call(["sed", "-i", "-r", "-e",
                                    expression,
                                    os.path.expanduser(filename)])